In July 1970 the British Board of Film Censors raised the age limit for X certificate films to 18. Although BBFC Secretary John Trevelyan believed that this would be sufficient to allow him to pass virtually all films submitted to the BBFC, the move coincided with a sharp increase in the number of films containing graphic scenes of sex and violence.

Trevelyan retired in 1971, handing his successor Stephen Murphy a poisoned chalice in the form of three hugely controversial British films: The Devils (d. Ken Russell), Straw Dogs (d. Sam Peckinpah) and A Clockwork Orange (d. Stanley Kubrick). All were made by respected directors, all had considerable artistic merit, but each pushed the envelope in terms of what had previously been considered acceptable.

A Clockwork Orange in particular became a political hot potato (Home Secretary Reginald Maudling requested a screening), and the focal point of concerted media and pressure-group campaigns attacking the film industry in general and Murphy's BBFC stewardship in particular, and subsequent high-profile releases such as Last Tango in Paris only served to fan the flames.

Murphy left the BBFC in 1975, and his successor James Ferman quickly put his own stamp on the Board, bringing film under the auspices of the Obscene Publications Act in 1977 and cracking down on sexual violence in particular, even recalling certain films (such as Emmanuelle (France, d. Just Jaeckin, 1974) for additional cutting.

Although Ferman was more lenient with films of clear artistic merit (especially if they were only likely to have limited releases), his hands were tied to a certain extent by existing legislation, augmented in 1978 by the Protection of Children Act. The latter, which covered scenes of unsimulated sexual activity involving children, did not admit context as a legal defence, and as a result even distinguished films like Pretty Baby (US, d. Louis Malle, 1978) and The Tin Drum (Die Blechtrommel, West Germany, d. Volker Schlöndorff, 1979) had to be cut.